Guardian on enchanter supports

I like the idea of Guardian on enchanters like Nami and Zilean, who may prefer to give one big shield on a larger cooldown than Aery's frequent smaller shields. Guardian is also more reliable for shielding in general, because it's easier to delay your ally-targeted spells than to keep Aery on hand by never damaging enemies. The 20% haste for you and your ally is also underrated in defensive situations.

However, I often find that Guardian is too easy to bait/waste in bot lane. If you preemptively cast it on your ally and they turn out to only take 50 poke damage, then most of their Guardian shield is wasted, your shield is completely wasted, both of your 20% hastes are wasted, and your keystone goes on a punishing 45 second cooldown while Aery/Aftershock supports walk all over you.

I'm proposing that we slightly increase the trigger window for Guardian, and that the shields for yourself/your ally trigger independently. Then, if only one of your shields activates, Guardian goes on a reduced cooldown. This would let more enchanter supports prioritize Guardian uptime on their adc if they're willing to keep back from trades themselves; importantly, this change shouldn't affect tanky supports who already like Guardian.

Thoughts?